Two major surface antigens on Trypanosoma cruzi have been identified (Nogueira, N., Chaplan, S., Tydings, J., Unkeless, J. and Cohn, Z., J. Exp. Med. 153 629 (1981)). One, a Mr 75,000 glycoprotein (GP) is specific for the culture forms (insect - host stages) of the organisms - epimastigotes and metacyclic trypomastigotes. The other, a Mr 90,000 GP is specific for vertebrate - host stages of the organisms (bloodstream - form trypomastigotes). The two GP are unrelated and do not cross react immunogeneically. Because of their specificity, the surface proteins are potential diagnostic markers for Chagas disease.